The SCUBA-2 Cosmology Legacy Survey: Multi-wavelength Properties of ALMA-identified Submillimeter Galaxies in UKIDSS-UDS

TL;DR

This study analyzes 52 submillimeter galaxies using multi-wavelength data, revealing their high redshifts, dense dust obscuration, and properties of their far-infrared emission, advancing understanding of dusty starburst galaxies.

Contribution

It provides the first detailed multi-wavelength characterization of ALMA-identified SMGs in the UKIDSS-UDS, including size, redshift, and dust properties, highlighting their extreme dust obscuration.

Findings

Median redshift of SMGs is 2.65, rising to 2.9 if optically faint.

SMGs have optically thick dust emission regions at wavelengths ≥75μm.

Median hydrogen column density is 9.8×10^{23} cm^{-2}, with V-band obscuration of 540 mag.

Abstract

We present a multi-wavelength analysis of 52 sub-millimeter galaxies (SMGs), identified using ALMA 870$\mu$m continuum imaging in a pilot program to precisely locate bright SCUBA2-selected sub-mm sources in the UKIDSS Ultra Deep Survey (UDS) field. Using the available deep (especially near-infrared), panoramic imaging of the UDS field at optical-to-radio wavelengths we characterize key properties of the SMG population. The median photometric redshift of the bright ALMA/SCUBA-2 UDS (AS2UDS) SMGs that are detected in a sufficient number of wavebands to derive a robust photometric redshift is $z$=2.65$\pm$0.13. However, similar to previous studies, 27% of the SMGs are too faint at optical-to-near-infrared wavelengths to derive a reliable photometric redshift. Assuming that these SMGs lie at z$\gtrsim$3 raises the median redshift of the full sample to $z$=2.9$\pm$0.2. A subset of 23, unlensed, bright AS2UDS SMGs have sizes measured from resolved imaging of their rest-frame far-infrared emission. We show that the extent and luminosity of the far-infrared emission are consistent with the dust emission arising from regions that are optically thick, on average, at a wavelength of $\lambda_0$$\ge$75$\mu$m (1-$\sigma$ dispersion of 55-90$\mu$m). Using the dust masses derived from our optically-thick spectral energy distribution models we determine that these galaxies have a median hydrogen column density of $N_{H}$=9.8$_{-0.7}^{+1.4}$$\times$10$^{23}$cm$^{-2}$, or a corresponding median $V$-band obscuration of $A_\mathrm{v}$=540$^{+80}_{-40}$mag, averaged along the line of sight to the source of their restframe $\sim$200$\mu$m emission. We discuss the implications of this extreme attenuation by dust for the multiwavelength study of dusty starbursts and reddening-sensitive tracers of star formation.